A UNITED NATIONS investigator says his team is close to prosecuting suspects behind a string of assassinations in Lebanon over the past two years, even as a political crisis sparked by the killings threatens to derail the investigation.

In a new report to the UN Security Council, the Belgian prosecutor Serge Brammertz said his team had identified the main suspects in the killing of the former Lebanese prime minister Rafiq Hariri in February last year. He is withholding their names to avoid prejudicing a trial.

Mr Hariri's murder sparked international condemnation and domestic protests that forced Syria to end its military occupation last year. But since then Damascus's power in Lebanon has grown once more.

Syria's main client in Lebanon, the Shiite guerilla group Hezbollah, has capitalised on shrinking US prestige since this year's 34-day war with Israel to demand a greater share of power in Beirut. Its critics say it is also trying to block the UN investigation into Mr Hariri's murder.

A Hezbollah-led opposition coalition staged a huge demonstration outside government buildings in Beirut on Sunday, and a tented protest camp has shut down part of central Beirut for two weeks.

Refusing to give in to Hezbollah's call for its resignation, the anti-Syrian government of the Prime Minister, Fouad Siniora, on Tuesday upped the stakes by approving a new tribunal to investigate the murders.

Mr Brammertz said his team is concentrating on identifying an unknown man suspected of detonating a huge car bomb in central Beirut as Mr Hariri's entourage was driving past.

Mr Brammertz said forensic examination of 33 small fragments of the man's body suggested the suspected killer "did not spend his youth in Lebanon but was situated there in the last two to three months before his death".